Open AccessA latitudinal gradient of beta diversity for exotic vascular plant species in North America
Author(s) -
Qian Hong
Publication year - 2008
Publication title -
diversity and distributions
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.918
H-Index - 118
eISSN - 1472-4642
pISSN - 1366-9516
DOI - 10.1111/j.1472-4642.2008.00466.x
Subject(s) - latitude , ecology , beta diversity , distance decay , spatial variability , spatial ecology , geographical distance , gamma diversity , altitude (triangle) , environmental gradient , geography , macroecology , physical geography , species richness , biology , statistics , habitat , mathematics , demography , population , geometry , geodesy , sociology
Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (ln S ) and spatial distance between pairs of state‐level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of ln S in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in ln S is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in ln S is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in ln S is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography.